1. Field of the Invention
The present invention generally relates to a scanning device, and more particularly to a scanning device capable of effectively ensuring a scanning quality.
2. The Related Art
In order to use, storage and publish documents more efficiently and conveniently, ordinary documents written or printed on papers would be converted to digital data by virtue of a scanning device for the convenience of follow-up application.
Referring to FIG. 1 and FIG. 2, the conventional scanning device includes a scanning platform 91, a feed roller 92 rotatably mounted above the scanning platform 91, and two coil springs 93 located under two ends of the scanning platform 91 to press the scanning platform 91 against the feed roller 92. In order to miniaturize the scanning device, a large paper feed tray and a document feeder are excluded from the scanning device. So, when one sheet-like medium needs to be scanned, it will be inserted into a paper-feeding inlet 90 of the scanning device with one edge thereof being against one end sidewall of the paper-feeding inlet 90 so as to ensure the sheet-like medium is transmitted straightly in the process of being scanned. For example, the right end sidewall of the paper-feeding inlet 90 is defined as a datum end for guiding the insertion of the sheet-like medium. One of the coil springs 93 near to the datum end is designated as a first coil spring, and the other one is designated as a second coil spring. The two coil springs 93 are symmetrically located about the centerline of the long side of the scanning platform 91, and they are selfsame.
In use, the sheet-like medium is inserted into the paper-feeding inlet 90 with one edge thereof being against the datum end. Because the two coil springs 93 press the scanning platform 91 to clamp the sheet-like medium between the scanning platform 91 and the feed roller 92, the feed roller 92 rotates to bring the sheet-like medium through the scanning device by virtue of friction force of the feed roller 92 acting on the sheet-like medium. At the same time, one side of the sheet-like medium is scanned by the scanning platform 91 to be converted into a digital image.
When a common paper document 94 is scanned by the scanning device, since it has very thin thickness of about 0.1 mm, approximately equal positive force can be acted on stress areas of the paper document 94 to keep the paper document 94 level in the process of being scanned (as shown in FIG. 1). However, when a small card 95 having a thicker thickness, such as an identity card and a bank card, is scanned by the scanning device, the scanning platform 91 will slant by taking a bottom corner of the card 95 away from the datum end as a fulcrum, due to the card 95 being hard and thick. As shown in FIG. 2, the selfsame coil springs 93 both press the scanning platform 91 to clamp the small card 95 between the scanning platform 91 and the feed roller 92, but different moment arms L1, L2 are formed because the small card 95 is small, hard and thick. As a result, the torque applied by the second coil spring is greater than that applied by the first coil spring so that causes the scanning platform 91 to rotate clockwise at a slight angle until balance. So, a separation is formed between the small card 95 and a part of the scanning platform 91 near to the datum end of the scanning device. It results in nonuniform friction force acted on the small card 95 by the feed roller 92. Finally, the scanning device gets an askew digital image of one side of the small card 95.
In view of these disadvantages above, the conventional scanning device needs to be improved.